Pain usually means something is wrong, but for people suffering from chronic pain — like from arthritis, cancer or other illnesses — powerful pain blockers are the only thing that help. Some chronic pain relievers block sodium channels, which are pathways in the nervous system that can generate pain signals. One of these blockers is probably familiar: Lidocaine, which you get at the dentist when you have a cavity that needs drilling. But blockers have to target the right channels. Other sodium channels affect your heart and other nerves, and you do not want a painkiller to interfere with those.